Technical Field
The present invention relates to a method of manufacturing a rotor for an electric rotating machine including a Lundell type rotor core, such as an alternator for a vehicle, and the rotor. In particular, the present invention relates to a method of dropping resin to a winding of a magnetic coil.
Related Art
As a rotor for an alternator for a vehicle, an assembly (Lundell type rotor core) is used in which cylindrical boss parts, disc parts, and a pair of iron cores (pole cores) are assembled so as to be opposed to each other. The disc parts extend in the radial direction from ends of the boss parts. The cores have a plurality of (e.g. eight) pawl parts extending from the peripheries of the disc parts in the direction toward other ends of the boss parts at an equal distance. V-shaped grooves (V-grooves) are formed between the adjacent pawl parts so as to reach the peripheries of the disc parts. The pawl parts of one of the cores are arranged in a state where the pawl parts are engaged with the V-grooves of the other of the cores via required clearances. Thereby, continuous clearances having a waveform shape are formed. A magnetic coil is accommodated inside the engaged pawl parts in a state where the magnetic coil is fitted to the boss parts from the outside. A shaft is pressed into a combination of a pair of the cores and the magnetic coil, thereby forming an integrated assembly.
The magnetic coil includes an insulating bobbin and a winding in which a conductive line is cylindrically wound around the insulating bobbin. A pair of the pole cores and the magnetic coil are integrated by pressing the shaft into the axis thereof. The insulating bobbin is manufactured by injection molding from resin such as nylon, and has a cylindrical drum around which the winding is wound, and flanges extending in the radial direction from the both ends of the drum.
Each of the flanges includes a collar part and tongue parts. The collar part is brought into contact with the inner face of the disc part of the pole core and the end face of the cylindrical winding. The tongue parts radially extend from the collar part so as to correspond to the plurality (e.g. six) of pawl parts and are brought into contact with the inner wall surfaces of the pawl parts. A V-shaped notch corresponding to the V-groove is formed between the adjacent tongue parts. In addition, one of the flanges is provided with a protrusion at a position of the bottom of the notch. The protrusion engages with the bottom part of the V-grooves (refer to Japanese Patent No. 4492303). The protrusions act as detents for the magnetic coil, while two of the protrusions opposed to each other act as locking parts, which lock outgoing lines of a winding start portion and a winding end portion of the winding, to prevent the winding from loosening.
In the assembly including the pair of the cores, the magnetic coil, and the shaft, a wavy groove (wavy clearance) is provided along the periphery of a pawl part having a cylindrical surface. In the wavy groove, the peripheries of both the disc parts are located at the bottoms of the V-grooves, and the periphery of a pawl part inside both the disc parts is formed with openings (windows) having a substantial parallelogram shape. The outer surfaces of the winding of the magnet coil are exposed from the windows. Thermoplastic resin, which covers the periphery of the winding and is impregnated into the winding, is applied from the wavy clearance to the assembly in an uncured state (in process of solation or gelation). The uncured resin applied to the winding is impregnated into the whole winding. Next, the uncured resin is heated in an air heating furnace for a predetermined time at a predetermined temperature, whereby the winding is thermally hardened and fixed.
In Japanese Patent No. 4492303, a method of impregnating resin into a rotor is disclosed which includes (a) heating process, (b) main impregnation process, and (c) thermal insulation fixing. As the main impregnation process, a technique is disclosed in which resin is dropped from a nozzle to a clearance between pawl parts (wavy clearance) while a rotor is rotated about an axis (shaft) in order to impregnate resin into the winding of the rotor.
In JP-A-2008-29102, a configuration is disclosed in which a bobbin of a rotor has a protrusion extending to the outside, and the protrusion engages with the bottom part of a V-groove of a pole core to prevent the rotation of the bobbin. According to this configuration, a problem has arisen that when resin is impregnated into a clearance between the protrusion and the bottom part of the V-groove and is fixed, a crack is generated in the protrusion, which lowers the electrical insulating properties of a magnetic coil.
JP-A-2007-151243 disclose a method of turning varnish (resin) into a gel by electrically heating a winding, and a drop impregnation method of dropping varnish to be impregnated, to improve reliability of a magnet coil. According to the method, a problem has arisen that when a large amount of varnish is dropped to the magnet coil in order to increase the amount of impregnation of varnish, the varnish overflows from a clearance between pawl parts, whereby a large amount of the varnish adheres to a pole core.
According to the drop impregnation method disclosed in JP-A-2007-151243, resin transfers on the surface of the winding and overflows to the pawl parts of the pole core. Thereby, the possibility, which is disclosed in JP-A-2008-29102, is easily increased that the resin is impregnated into the clearance between the protrusion and the bottom part of the V-groove and is fixed.
The technique, in which uncured resin having fluidity is dropped from a nozzle to a clearance between pawl parts (wavy clearance) while a rotor is rotated about an axis (shaft) in order to impregnate resin into the winding of the rotor, has high productivity. However, a large amount of resin to be spread and penetrated to the whole winding flows to a narrow area immediately below the drop. Hence, problems easily arise that resin dropped around the tip of the pawl of the pole core is impregnated to a clearance between the protrusion of the bobbin and the bottom part of the V-groove of the pole core, as disclosed in JP-A-2008-29102, and that the dropped uncured resin overflows and adheres to the pole core, as disclosed in JP-A-2007-151243.